Typically, integrated circuits include a passivation layer formed over a top surface of the integrated circuit. Generally, the passivation layer is an insulating, protective layer that prevents mechanical and chemical damage during assembly or packaging of the integrated circuit. In addition, the passivation layer can protect sensitive circuitry located on the top surface of the integrated circuit from damage due to moisture. The passivation layer should be impermeable to moisture, as moisture is one of the catalysts for corrosion of electrical interconnections and circuitry of integrated circuits.
FIG. 1 shows a prior art integrated circuit image sensor array. The integrated circuit image sensor array includes a substrate 100. An interconnection structure 110 is formed adjacent to the substrate 100. A pixel interconnect structure 120 is formed adjacent to the interconnection structure 110. Several layers 130 are formed over the pixel interconnect structure 120 which form an array of image sensors. Generally, electrodes 140, 142, 144 form cathodes of the image sensors. A transparent conductor 150 is formed adjacent to the layers 130 which form the array of image sensors. The transparent conductor 150 provides biasing of the anodes of the image sensors.
Typically, the interconnection structure 110 is a standard CMOS interconnection structure. The interconnection structure includes conductive vias 114, 116, 118 which provide electrical connections to the substrate 100.
The pixel interconnect structure 120 provides reliability and structural advantages to the elevated image sensor structure. The pixel interconnect structure 120 allows for the formation of thin pixel electrodes 140, 142, 144 because the pixel electrodes 140, 142, 144 are formed over silicon rather that a metal pad located on the interconnection structure 110. The pixel interconnect structure 120 electrically connects the pixel electrodes 140, 142, 144 to the interconnection structure 110. The pixel interconnect structure 120 is typically formed from a dielectric film, for example, polyimide, silicon oxide or a silicon nitride.
The pixel interconnect structure 120 of FIG. 1 does not provide protection of the conductive vias 114, 116, 118, or electrical circuitry located on the substrate 100 from moisture. Therefore, the conductive vias 114, 116, 118 and the electrical circuitry located on the substrate 100 are susceptible to corrosion.
Generally, the top surface of a passivation layer of a typical integrated circuit is not planar. That is, the top surface is not a well controlled flat surface. Therefore, a typical passivation layer cannot be sandwiched between layers of the integrated circuit image sensor array of FIG. 1.
High temperatures are required to form a passivation layer. Generally, the temperatures required to form the passivation layer are greater than the temperature that most sensors can withstand without being damaged. Therefore, a passivation layer cannot be formed over the integrated circuit image sensor array of FIG. 1. Additionally, a passivation layer formed over an integrated circuit image sensor array could absorb light before the light is absorbed or sensed by the image sensor array.
It is desirable to have a passivation structure formed over a substrate, which includes conductive vias which pass through the passivation structure so that image sensors can be located over the passivation structure and electrically connected to the substrate. It is further desirable that the passivation structure include a planar surface to allow the passivation layer to be sandwiched between the image sensors and the substrate.